1868, "line drawn from point to point, so that its direction is everywhere that of the motion of the fluid" [Lamb, "Hydrodynamics," 1906], from stream (n.) + line (n.). The adjective is attested from 1898, "free from turbulence," 1907 in sense of "shaped so that the flow around it is smooth."

v.

1913, "give a streamline form to," from streamline (n.). From 1936 in the extended sense of "simplify and organize." Related: Streamlined; streamlining.